fix #2847: api: datastore: change backup owner

This adds an api method to change the owner of
a backup-group.

Signed-off-by: Dylan Whyte <d.whyte@proxmox.com>

src/config/cached_user_info.rs

@@ -96,9 +96,7 @@ impl CachedUserInfo {
         }
         Ok(())
     }
-}
 
-impl CachedUserInfo {
     pub fn is_superuser(&self, userid: &Userid) -> bool {
         userid == "root@pam"
     }